A unique subspecies of rhino, Rhinoceros sondaicus annamiticus, is entirely extinct. The disappearance itself occurred in 2010, but it was only last October that zoologists were able to confirm what they had feared.

Historically, there have been three subspecies of the one-horned Javan rhinoceros. The first to disappear was Rhinoceros sondaicus inermis, a variety that roamed India, Bangladesh, and Myanmar until a century ago. Now the beast has lost its foothold in Vietnam, leaving only Rhinoceros sondaicussondaicus in Indonesia. We are despairingly close to losing the species altogether. The IUCN listing for this critically-endangered mammal, last updated in 2008, notes that fewer than 50 exist in the wild, constantly threatened by poaching and confined to such a small area that the rhinos may not even be able to maintain anything more than a meager population.

The Javan rhino is on death watch. And given how closely zoologists have been monitoring the ever-weakening vital signs of the species, it’s unsurprising that we know about the extinction of Rhinoceros sondaicus annamiticus in depressing detail.

WWF Vietnam biologist Sarah Brook and colleagues documented the fate of the rhino in the October, 2012 issue of Biological Conservation. The tale is doubly tragic because the Javan rhino was thought to be entirely absent from Vietnam until a hunter killed one in 1988. Subsequent searches by zoologists showed that a relict, genetically-distinct population of 10-15 individuals survived within what became Cat Tien National Park. As the years went by, however, surveys found fewer rhinos. By 2002, it seemed that there were only as many as six, and perhaps as few as one, Javan rhino left in the park.

To get a handle on how many Javan rhinos might survive in Vietnam, Brook and collaborators employed scat-detecting dogs to track down rhino dung within the 25 square miles of the “rhinoceros core area”, plus 21 square miles outside the focus area, during three searches between October 27th, 2009 and April 8th, 2010. The aim was to find rhino feces that could be genetically sampled and analyzed to determine how many individuals were left within the swath of bamboo forest. In addition to relocating rhinoceros wallows and tracks, the survey found 22 rhinoceros dung piles.

Prospects for the forest’s rhinoceros looked grim. As the paper states in the deadpan tone required of academic literature, “Notably, no new dung piles were found after 4th February, for the last 9 weeks of the survey and no fresh footprints were found after mid February.” The trail had gone cold. And when the researchers analyzed the 17 fecal samples that yielded data, they found the genetic signature of only one rhinoceros – a DNA match to a dead rhino that was discovered right as the survey finished. That rhino had been killed by poachers, a bullet wound and a missing horn leaving no doubt as to its fate.

The rhinoceros, probably the last of its kind, had perished months before. “[D]ue to the absence of most of the skin and soft tissue which had already decomposed,” Brooks and collaborators report, “it is therefore suspected from the field data that the last rhinoceros died in late January/early February 2010.”

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Paleontologists are familiar with a phenomenon called the Signor-Lipps effect – the quirks of the fossil record may not preserve the very last individual of a species, frustrating our attempts to detect the refined pattern of extinction. But neontologists can see modern extinctions in terrifying detail, sometimes, as in this case, down to the last individual of a population.

Bit by bit, and individual by individual, rare creatures are slipping away. The Javan rhinoceros that died within Cat Tien National Park was probably the last of its kind, giving us the sorrowfully precise time of death for a unique beast. The study’s conclusion that the “findings are disheartening and point to ongoing conservation failures in the region” is a restrained expression of a painful truth.

The methods that confirm the Javan rhino’s extirpation can still be used to track and conserve other megafauna. Scat-detecting dogs, genotyping feces, and analyzing bacterial diversity in scat are effective conservation tools that can be employed to monitor mammal populations elsewhere. For rhinos, there is no time to waste. As zoologist Darren Naish lamented, 2012 was a “horrific year” for rhinos, with over 455 African rhinos killed within a year. The situation is so dire that thieves are even stealing rhino horns from museums, the New York Times reports, to fuel a black market trade which caters to unscrupulous, wealthy individuals who see rhino horns as nothing more than status symbols.

We may very well lose the world’s last rhinos. Extinction is bearing down on these thick-skinned perissodactyls so fast that it’s unclear whether they will ever recover. And if we let them die, the loss cuts deeper than single species or genera. We lose entire groups of organisms that carry on ancient evolutionary legacies.

Consider the Sumatran rhinoceros, Dicerorhinus sumatrensis, another critically-endangered species represented by less than 250 adult animals living in small, scattered populations from Myanmar to Borneo. This hairy rhino superficially resembles other Asian rhinos, but is actually more closely-related to the woolly rhinoceros of the Pleistocene. The lineage of the last shaggy rhino diverged from those of all other living rhinos about 25 million years ago.

If we destroy the Sumatran rhino, we lop off an entire branch of evolution’s fantastic tree of Life and lose yet another connection to prehistory. And if we lose all rhinos, then a 45 million year old epic comes to an end. Extinction not only erases an animal’s future. It severs connections to nature’s past.

It’s also worth noting that the Vietnamese subspecies of the Javan rhino wasn’t originally restricted to Vietnam, but was simply the last surviving population after it had died out elsewhere in mainland Southeast Asia, from Cambodia, Laos, and Thailand, into the Malay Peninsula. It’s trafic how both the Sumatran and Javan rhinos were once widely distributed across Southeast Asia, only to have suffered such a severe contraction in range as a result of hunting and habitat loss.

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